Hi,

I am hoping that someone can just magically point out the cap I need to replace to fix this issue. I don’t have any board schematics for the s90ES so those would be cool to!  edit: link to schematics below, and a crappy photo of my board

I’ve troubleshot some:

Pan hard left/right works evenly and fine with HP out.

L/Mono Out is attenuated by about half (total guess but it’s a lot and unworkable) to R Out.

I’ve a saved profile so I factory defaulted 2x, no change in symptoms.

I tried to map something to the assignable outs to see if they might get involved but after going from pg9 to page 63 to page 154 and back, I can’t figure that out and I doubt they are. Although I’d try if someone could walk me through that as if I was a small toddler.

I haven’t removed the board from the frame yet, but I’m looking at it. Two larger caps (gold-ish) that are physically close to the outs are both a bit bulge-y. I will probably just replace them both as a first attempt, but any thoughts are welcome!

Thanks for being here!

Scott

hey look! link to a crappy phone photo of the I/O board:

https://drive.google.com/file/d/1spU9aoit9IeSjz1FO0KMq2qLaLKvUN8L/view?usp=sharing

and here is the schematic, I did find it:

https://drive.google.com/file/d/1mR-1Z22GoQoN-b_0vQTtYJVJ8ISpEv9C/view?usp=sharing

consolidated info into OP

consolidated part2

Welcome to the forum.

Due to my limited internet access, I can’t access your links. I don’t know what schematic you found, but just in case here’s a link to the service manual:
https://elektrotanya.com/yamaha_s-90.pdf/download.html

If changing the bulging caps doesn’t help (line output coupling R=C142, L/MONO=C143, 47µF/50V), then a leaky output muting transistor is a possibility. See this thread…
http://www.motifator.com/index.php/forum/viewthread/475333
...which concerns a Motif XF, but the issue is similar. In the S90ES the devices are R=TR106, L/MONO=TR107, 2SC2878. Check for DC as described in the linked thread. The muting transistors are a special type, generic replacements won’t do.

5pinDIN - 16 November 2020 10:53 PM

Welcome to the forum.

Thanks!

Due to my limited internet access, I can’t access your links. I don’t know what schematic you found, but just in case here’s a link to the service manual:
https://elektrotanya.com/yamaha_s-90.pdf/download.html

I did find the s90es service manual.

If changing the bulging caps doesn’t help (line output coupling R=C142, L/MONO=C143, 47µF/50V), then a leaky output muting transistor is a possibility. See this thread…
http://www.motifator.com/index.php/forum/viewthread/475333
...which concerns a Motif XF, but the issue is similar. In the S90ES the devices are R=TR105, L/MONO=TR107, 2SC2878. Check for DC as described in the linked thread. The muting transistors are a special type, generic replacements won’t do.

Ok, so I changed the bulging caps, but they weren’t the two you referred to. C142/143 look fine. I could order them and replace anyway for fun, but the bulging ones were the larger nichicons at c102/103. No change in symptoms with swap.

I do have a symptom at the HP out. I’m not sure to what extent because I’ve lived with it for so long. If the main volume slider is 75% up or more, I get a good amount of intermittent noise there. I will check DC tomorrow. On the chance that it is/are the muting transistors it seems that Abacus Tech in Naples might have some. They have stated stock for the 2SC2878, but they show no stock in the variants A and B. My transistors, on the board not in the schematic from the service manual, show an “A” and “5H” under the number. The service manual shows this:

2SC2878 A,B TP

Any thoughts on that? I could just throw em in and try, if the DC test is positive and I won’t destroy anything.

Thanks so much for your attention, I’m very much a newbie at attempting these repairs but I can handle caps, transistors, and switches so far :)

Too many options!

http://www.sierraic.com/2SC2878?utm_source=octopart&utm_medium=cpc&utm_campaign=octopart_2019&utm_term=2SC2878

Before I forget...
I had a typo above and corrected it - Right channel muting transistor is TR106.

 

wynter - 19 November 2020 10:11 PM

Ok, so I changed the bulging caps, but they weren’t the two you referred to. C142/143 look fine. I could order them and replace anyway for fun, but the bulging ones were the larger nichicons at c102/103. No change in symptoms with swap.

C102/103 are output coupling for the PHONES.

 

wynter -

I do have a symptom at the HP out. I’m not sure to what extent because I’ve lived with it for so long. If the main volume slider is 75% up or more, I get a good amount of intermittent noise there. I will check DC tomorrow.

The PHONES outputs also have muting transistors, TR100/101.

 

wynter -

On the chance that it is/are the muting transistors it seems that Abacus Tech in Naples might have some. They have stated stock for the 2SC2878, but they show no stock in the variants A and B. My transistors, on the board not in the schematic from the service manual, show an “A” and “5H” under the number. The service manual shows this:

2SC2878 A,B TP

Any thoughts on that? I could just throw em in and try, if the DC test is positive and I won’t destroy anything.

I’ve had no problem using Toshiba 2SC2878 devices. (See https://pdf1.alldatasheet.com/datasheet-pdf/download/549004/TOSHIBA/2SC2878A.html) Note that the Emitter-base voltage, hFE and on-resistance are not common. Other manufacturers of 2SC2878 transistors may not meet those specs. An example that doesn’t is the Secos product (http://www.secosgmbh.com/datasheet/products/SSMPTransistor/TO-92/2SC2878A.pdf)

On a temporary basis, you could just remove the muting transistors and see if things improve. However, be aware that without them there may be significant turn-on/off transients (pops,etc.). DO NOT have amps turned up or headphones on your ears at power-up/down if you try this.

 

wynter -

Thanks so much for your attention, I’m very much a newbie at attempting these repairs but I can handle caps, transistors, and switches so far :)

You’re welcome.
Have fun, cautiously. :-)